Fig. 8

VoNPs still elicited protective immunity in mice after 180 days of storage. a The bar represents the titers of the anti-Vo IgGs in the mice immunized with the VoNPs and Vo  + Al, which were stored at 4 °C for 180 days. b The bar represents the survival of the mice after challenge with a lethal dose of E. coli K1 RS218. Before the challenge, the mice were immunized with the VoNPs or Vo + Al aliquots that had been stored at 4 °C for 180 days. c Mice were immunized with VoNPs or Vo + Al, which were stored at 4 °C for 180 days. The bar represents the body weight of the mice after challenge with a sublethal dose of E. coli K1 RS218. d The bar represents the number of bacteria per ml blood 48 h after a sublethal challenge with E. coli K1 RS218. e The bar represents the number of bacteria per gram of spleen tissue 48 h after a sublethal challenge with E. coli K1 RS218. BNP indicates the blank nanoparticle control. n.s. no significant difference; *P < 0.05